I have a 1949 Airstream Trailwind with a tube frame (the frame is actually in very good shape). The trailer is currently going through a total renovation which includes a new axel. I've read many accounts where the tube frame has been replaced or at least shored up during renovation. I'd appreciate your opinions from both those who have replaced/shored up the frame and those who haven't to better assess the path forward.

If the pipe is structurally sound I see no problem with using that original set up. Rust out is another subject....as it is with a ladder frame.
There are enough formed aluminum cross members to support any reasonable installations topside. The floor is a major contributor to strength. I would go with a 3/4 instead of the original 1/2 plywood. You will run into some other interesting problems like propane bottle mounts, sway control , turning radius
and jack....all part of the process.
On your little baby....I'd stay with the pipe unless expense is not a problem.

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__________________"If it can't be reduced, reused, repaired, rebuilt, refurbished, refinished, resold, recycled or composted then it should be restricted, redesigned or removed from production."

If the pipe is to remian, and I would keep it,
1. fabricate better pipe to rib connections. Yours has simple tabs. In my 1950, it had a bracket that circled the pipe and provided much better connection.
2. Create a connection between side steel channels that the running gear is attached to and to a V towards the hitch. In David Winick's boot he illustrates his redo of a trailwind and has this mod made.
3. the pipe will limit the size of any one holding tank if you choose to place any below the floor.
4. if you integrate a steel frame it will give you places to hang tanks, mount stabilizing jacks, etc. The Aluminum ribs are not good choices for this as they are just .032 sheet.
5. If you go with thicker plywood, you will add about 30lbs per sheet of plywoord per extra 1/4 inch. It may not seem like much, but remeber that each little bit adds up with all your upgrades and mods.

Thank you for your input and your point is well taken. We are planning to stay pretty true to the basic design maintining the original woodwork and sink/counter. We will replace the existing mattress with a foam bed but that may actually save weight. There will be some weight gain from adding a small refrigerator, a horseshoe couch at the front and a low profile heater/airconditioner. If we add tanks they will be on the small side so overall the increased weight should not be excessive. I like your thought that less is more. I'd be happy if you would check back in June (targetted completion date) and see where we end up.